The present invention relates to a human-modeled hand mechanism which can be used as a substituting mechanism for performing various kinds of work manually carried out by human workers, and, more particularly, it relates to a human-modeled articulated hand for use as an endeffector for robots, artificial arms and various manipulators.
Heretofore, endeffectors (hands) for use in industrial robots have been put into practice as one of the apparatus of the type as described above. In most cases, the endeffectors have a structure in which two flat plates are arranged opposite each other and operated through link mechanisms, straight-driving guide mechanisms, and the like. In the case where the kind of objects to be grasped is decided beforehand, endeffectors of the kind having the form suitable to the kind of the objects are used. In the case where various kinds of objects are dealt with, on the other hand, interchangeable endeffectors are used.
However, the former is short of generalization, flexibility and adaptability to be required of robots, and the latter has limitations, such as a structural limitation in which the endeffectors must be interchangeable, a limitation in which endeffectors for replacement must be prepared in the vicinity of the respective robot, and the like.
On the other hand, five-finger hands, three-finger hands and the like are under investigation and development. The field to which the hands of this type are mainly applied is a field of artificial hands. That is to say, an object of the hand of this type is to imitate a human hand. The five-finger hand is designed to imitate a human hand in such a manner that a first finger or thumb is opened and closed by a hydraulic actuator while other fingers constituted by link mechanisms are bent and stretched in pairs at once through a pulse motor. However, such a five-finger hand has the following structural disadvantages: 1) the articulates of the hand cannot be driven independently because the articulates of the fingers are linked; 2) a hydraulic pump must be provided separately because a hydraulic actuator is used for opening and shutting the thumb; 3) the grasping force of the hand is little because optimum torque cannot be given to every shaft because the driving source is constructed by one pulse motor; and the like.
Therefore, three-finger hands improved to move articulates independently of each other have been proposed. The hand of this type has a structure in which pulleys of respective articulates are driven independently of each other by wire ropes passed into sleeves. However, such a hand has the following disadvantages: 1) the load imposed on each wire rope acting as a power transmittng means is so large that accuracy in positioning as well as in force control is lowered by the expansion of the wire rope, because the torque and angle of each articulate cannot be detected; 2) the loss of power of the wire rope is so large that the grasping force of the hand cannot be increased, because the hand is far from the driving source and a wire rope provided with a sleeve is used as the power transmittng means (the more the diameter of the wire rope increases, the more the loss of power increases); 3) because the sleeve cannot be bent in large curvature, the wire rope-sleeve mechanism can hardly be set in a robot or interferes with work; 4) because the wire rope is used in combination with sleeve, the friction therebetween is large when the sleeve is bent in large curvature; and the like. In an alternatively proposed multi-finger hand, fingers are connected with each other coaxially in multi-stages through link mechanisms each having a ball screw as its one side; and a worm gear, a wire and the ball screw are connected in order to form a power transmitting system (Japanese Unexamined Patent Publication No. 62-124892). This structure, however, has the following disadvantages: 1) because the power transmitting system is so complex in construction that the loss of power is large, speed-reduction mechanisms in the power transmitting means, such as a worm gear and a ball screw, are inferior in reversibility of power transmission, so that the mechanisms can hardly be operated from the side of the hand though they can be operated from the side of the motor; 2) because the finger cannot be elastically bent though external force acts on the top of the finger, the hand cannot be applied to the case where the subject is fragile; 3) because the relationship between the first and second fingers is fixed, objects to be grasped are limited; and the like.